This patch adds both normal PM suspend/resume support and runtime PM
support to pl330 DMA engine driver.

The runtime power management for pl330 DMA driver allows gating of AMBA
clock (PDMA) in FSYS clock domain, when the device is not processing any
requests. This is necessary to enter low power modes on Exynos SoCs
(e.g. LPA on Exynos4x12 or W-AFTR on Exynos3250).

Runtime PM resuming of the device may happen in atomic context (during
call device_issue_pending()) so pm_runtime_irq_safe() is used. This will
lead only to disabling/enabling of the clock but this is sufficient for
gating the clock and for reducing energy usage.

During system sleep the AMBA bus clock is also unprepared.

Suggested-by: Bartlomiej Zolnierkiewicz <redacted>
Signed-off-by: Krzysztof Kozlowski <redacted>
---
 drivers/dma/pl330.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 4839bfa74a10..9c014874c33d 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c

@@ -27,6 +27,7 @@
 #include <linux/of.h>
 #include <linux/of_dma.h>
 #include <linux/err.h>
+#include <linux/pm_runtime.h>

 #include "dmaengine.h"
 #define PL330_MAX_CHAN         8

@@ -1958,6 +1959,7 @@ static void pl330_tasklet(unsigned long data)
        struct dma_pl330_chan *pch = (struct dma_pl330_chan *)data;
        struct dma_pl330_desc *desc, *_dt;
        unsigned long flags;
+       bool power_down = false;

        spin_lock_irqsave(&pch->lock, flags);

@@ -1972,10 +1974,17 @@ static void pl330_tasklet(unsigned long data)
        /* Try to submit a req imm. next to the last completed cookie */
        fill_queue(pch);

-       /* Make sure the PL330 Channel thread is active */
-       spin_lock(&pch->thread->dmac->lock);
-       _start(pch->thread);
-       spin_unlock(&pch->thread->dmac->lock);
+       if (list_empty(&pch->work_list)) {
+               spin_lock(&pch->thread->dmac->lock);
+               _stop(pch->thread);
+               spin_unlock(&pch->thread->dmac->lock);
+               power_down = true;
+       } else {
+               /* Make sure the PL330 Channel thread is active */
+               spin_lock(&pch->thread->dmac->lock);
+               _start(pch->thread);
+               spin_unlock(&pch->thread->dmac->lock);
+       }

        while (!list_empty(&pch->completed_list)) {
                dma_async_tx_callback callback;

@@ -1990,6 +1999,12 @@ static void pl330_tasklet(unsigned long data)
                if (pch->cyclic) {
                        desc->status = PREP;
                        list_move_tail(&desc->node, &pch->work_list);
+                       if (power_down) {
+                               spin_lock(&pch->thread->dmac->lock);
+                               _start(pch->thread);
+                               spin_unlock(&pch->thread->dmac->lock);
+                               power_down = false;
+                       }
                } else {
                        desc->status = FREE;
                        list_move_tail(&desc->node, &pch->dmac->desc_pool);

@@ -2004,6 +2019,10 @@ static void pl330_tasklet(unsigned long data)
                }
        }
        spin_unlock_irqrestore(&pch->lock, flags);
+
+       /* If work list empty, power down */
+       if (power_down)
+               pm_runtime_put(pch->dmac->ddma.dev);
 }

 bool pl330_filter(struct dma_chan *chan, void *param)

@@ -2073,6 +2092,7 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned

        switch (cmd) {
        case DMA_TERMINATE_ALL:
+               pm_runtime_get_sync(pl330->ddma.dev);
                spin_lock_irqsave(&pch->lock, flags);

                spin_lock(&pl330->lock);

@@ -2099,10 +2119,14 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
                        dma_cookie_complete(&desc->txd);
                }

+               if (!list_empty(&pch->work_list))
+                       pm_runtime_put(pl330->ddma.dev);
+
                list_splice_tail_init(&pch->submitted_list, &pl330->desc_pool);
                list_splice_tail_init(&pch->work_list, &pl330->desc_pool);
                list_splice_tail_init(&pch->completed_list, &pl330->desc_pool);
                spin_unlock_irqrestore(&pch->lock, flags);
+               pm_runtime_put(pl330->ddma.dev);
                break;
        case DMA_SLAVE_CONFIG:
                slave_config = (struct dma_slave_config *)arg;

@@ -2138,6 +2162,7 @@ static void pl330_free_chan_resources(struct dma_chan *chan)

        tasklet_kill(&pch->task);

+       pm_runtime_get_sync(pch->dmac->ddma.dev);
        spin_lock_irqsave(&pch->lock, flags);

        pl330_release_channel(pch->thread);

@@ -2147,6 +2172,7 @@ static void pl330_free_chan_resources(struct dma_chan *chan)
                list_splice_tail_init(&pch->work_list, &pch->dmac->desc_pool);

        spin_unlock_irqrestore(&pch->lock, flags);
+       pm_runtime_put(pch->dmac->ddma.dev);
 }

 static enum dma_status

@@ -2162,6 +2188,15 @@ static void pl330_issue_pending(struct dma_chan *chan)
        unsigned long flags;

        spin_lock_irqsave(&pch->lock, flags);
+       if (list_empty(&pch->work_list)) {
+               /*
+                * Warn on nothing pending. Empty submitted_list may
+                * break our pm_runtime usage counter as it is
+                * updated on work_list emptiness status.
+                */
+               WARN_ON(list_empty(&pch->submitted_list));
+               pm_runtime_get_sync(pch->dmac->ddma.dev);
+       }
        list_splice_tail_init(&pch->submitted_list, &pch->work_list);
        spin_unlock_irqrestore(&pch->lock, flags);

@@ -2585,6 +2620,34 @@ static int pl330_dma_device_slave_caps(struct dma_chan *dchan,
        return 0;
 }

+/*
+ * Assume that IRQ safe runtime PM is chosen in probe and amba bus driver
+ * will only disable/enable the clock in runtime PM suspend/resume.
+ */
+static int __maybe_unused pl330_suspend(struct device *dev)
+{
+       struct amba_device *pcdev = to_amba_device(dev);
+
+       if (!pm_runtime_suspended(dev))
+               amba_pclk_disable(pcdev);

+
+       return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(pl330_pm, pl330_suspend, pl330_resume);
+
 static int
 pl330_probe(struct amba_device *adev, const struct amba_id *id)
 {

@@ -2738,6 +2801,9 @@ pl330_probe(struct amba_device *adev, const struct amba_id *id)
                pcfg->data_buf_dep, pcfg->data_bus_width / 8, pcfg->num_chan,
                pcfg->num_peri, pcfg->num_events);

+
        return 0;
 probe_err3:
        /* Idle the DMAC */

@@ -2764,6 +2830,8 @@ static int pl330_remove(struct amba_device *adev)
        struct pl330_dmac *pl330 = amba_get_drvdata(adev);
        struct dma_pl330_chan *pch, *_p;

+       pm_runtime_get_noresume(pl330->ddma.dev);
+
        if (adev->dev.of_node)
                of_dma_controller_free(adev->dev.of_node);

@@ -2802,6 +2870,7 @@ static struct amba_driver pl330_driver = {
        .drv = {
                .owner = THIS_MODULE,
                .name = "dma-pl330",
+               .pm = &pl330_pm,
        },
        .id_table = pl330_ids,
        .probe = pl330_probe,
--

1.9.1